Technical Abstract:
Lacewings (Chrysopidae: Neuroptera) are a family of insect predators, also called aphidlions because of their voracious feeding on aphids. While lacewings have been popular with growers, gardeners, and biological control scientists, they have had little visibility in the world of genetics. Generalist predators have been essentially ignored from a genetic standpoint. Insectivory is a rather important part of the insect world, and terribly important from an environmental standpoint, and certainly worth genetic investigation. The recent completion of the aphid genome almost demands the initiation of an effort to sequence a generalist predator of aphids so that predator/prey genetic interactions can be examined. Based on this reasoning I propose that a lacewing, Chrysoperla rufilabris is an overlooked insect model organism, and should be added to the list of organisms scheduled for rigorous genetic study and genomic sequencing. Lacewings belong to the order Neuroptera which has no representatives in nuclear genome projects. The order is genetically represented by very few nucleotide, EST, or protein sequences. Therefore a genetic model in this order would add substantially to the resources available to the systematics, phylogenetics, and evolution communities. The order is primitively holometabolous and should be studied as an evolutionary transition organism from the hemimetabolous insects (such as the pea aphid) to the apex holometabolous orders (Diptera, Lepidoptera, Coleoptera, and Hymenoptera). Initial molecular genetic sequencing could focus on several broadly representative sets of expressed sequences from the developmental stages of the insect and adult males, virgin and gravid females, and possibly specific body parts or tissues.
Lacewings may be ideal candidates as subjects of genetic study. They are amenable to mass rearing. The techniques used in mass rearing can be scaled down to small-scale rearing quite easily. While the lifecycle is not as short as Drosophila, under ideal conditions a generation of lacewings is about 30 days, and most species are multivoltine, requiring no diapause in culture. They fare well in small spaces if reasonably good humidity can be maintained and using a standard dark: light cycle (we use 8:16). Eggs of most lacewings, and certainly the commercially produced species, are laid individually on almost any surface, continually during the fecund portion of the female’s adult lifespan, and have stalks. Thus they are both plentiful and easy to harvest. While eggs are not entirely transparent, they are sufficiently translucent to observe embryo development. Anterior and posterior are easily observed by the presence of stemmata or eyespots in later embryonic development. The egg stalk is attached at the posterior end of the egg, and there is a distinctive micropyle at the anterior end of the egg providing visible external reference at the very earliest possible developmental timing. Dorsal and ventral can also be identified on the developing egg because the embryonic germ band is easily identifiable. The chorion is soft and can be pierced with a microinjection needle. Embryonic development is rather slow, taking around 7 days. This would make the organism useful for developmental biologists interested in gene expression and signaling pathways. Larvae are not transparent, but can be handled easily. There are multiple larval instars (generally 3) leading up to a cessation of feeding, cocoon spinning and pupation. Pupae can be separated from the cocoon, using sufficient dexterity, and the pupa is moderately translucent. The adult stage is also translucent. Male and female adults can be easily identified and separated prior to mating for individual pair matings. Furthermore, the adult lifespan is long enough (often two months or more) that mating a parent to offspring is also possible. Adults fly, but weakly and are generally easy to handle. Once fertilized a gravid female produces eggs continually, sometimes for >30 days, producing up to 1200-1400 eggs. At least one highly inbred culture is available from our USDA ARS laboratory.